1. Field of the Invention
The present invention relates to a signal processing circuit for a switch capable of reducing insertion loss and, more particularly, to a signal processing circuit for a switch capable of reducing insertion loss in a portable radio communication apparatus capable of increasing conversation time and of reducing weight.
2. Description of the Related Art
A portable radio communication apparatus needs a high frequency switch capable of switching high frequency signal paths between at least one high frequency power amplifier and antennas, because the portable radio communication apparatus uses an external antenna when it is set in a mobile mode and an internal antenna when it is carried by a person.
In the portable radio communication apparatus, a prerequisite of the high frequency switch is to minimize an insertion loss of the high frequency switch in order to increase conversation time and reduce weight. The minimizing of the insertion loss leads to reducing an output power of the power amplifier. As a result, current consumption is reduced, while conversation time is increased. Moreover, since a high power output is not needed from the power amplifier, a small and light power amplifier is available.
A conventional high frequency switch is implemented by a combination of transistors, diodes or similar semiconductor devices to promote light weight and small size configuration. Such a high frequency switch is described in, for example, Japanese Patent Laid-Open No. 80974/1984 (JP-A-59-80974). This high frequency switch has a gate switch FET implemented by a GaAs FET between a switch FET and a terminating FET to have a small insertion loss and enhanced isolation. The high frequency switch uses a zero voltage and a negative voltage as a high voltage and a low voltage for switch control signals.
Therefore, the use of the high frequency switch described in JP-A-59-80974 has been considered for use in the portable radio communication apparatus in order to achieve small insertion loss. However, in the portable radio communication apparatus, it is difficult to provide a negative voltage generator exclusively for the high frequency switch due to limitations therein, for example, packaging constraints.